This invention is generally directed to packaged or configured electrical components, such as very large scale integrated circuit (VLSI) chips, situated in a high density interconnect (HDI) structure. More particularly, the present invention relates to electrical circuit modules, such as integrated circuit modules, and a method of making the same, in which moisture is prevented from penetrating the module and reaching the electrical circuit components within the module.
HDI structures of the type mentioned above are shown and described in U.S. Pat. No. 4,783,695, "Multichip Integrated Circuit Packaging Configuration and Method," issued Nov. 8, 1988, and in U.S. Pat. No. 4,918,811, "Multichip Integrated Circuit Packaging Method," issued Apr. 24, 1990, both assigned to the assignee of the present invention and herein incorporated by reference. Such HDI structures, which may be built up in an integrated circuit module by means of multiple ply sequences stacked over the chips and the substrate, are subject to moisture penetration. In such a module each sequence includes at least a dielectric film and a metal layer which overlies the film and which makes the desired interchip and intrachip connections. Moisture that penetrates the module may corrode these connections, or contaminate the chips themselves, and reduce the overall reliability of the module.
Various measures have been devised to protect modules from such damage, such as placing the module inside a metal enclosure. Aside from its relatively high cost, a metal enclosure adds bulk and weight, offsetting some of the salient advantages associated with use of an HDI structure In accordance with another protection technique, the module is surrounded with a material, such as polymer. However, experience has shown that a polymer material is susceptible to moisture penetration on the molecular level.